Welding system



Jan. 18, 1949.

J. H. ENGLAND WELDING SYSTEM Filed Ma 28, 1945 47 uuounun Patented Jan. 18, 1949 UNITED STATES PATENT OFFICE WELDING SYSTEM Application May 28, 1945, Serial No. 596,120

13 Claims.

This invention relates to a welding system and more particularly to a welding system in which electrical energy is stored in a condenser and subsequently discharged into a welding load circuit to supply the welding current to a resistance welding load.

In systems of the type to which the invention relates, the condenser is charged from a suitable source of rectified current. It is desirable that this source. of charging current be controlled so that the condenser can be charged to a definite predetermined value in order that the energy supplied to the load will not vary from the predetermined value. Systems have heretofore been proposed for regulating the voltage to which the condenser is charged. However, where such systems are dependent solely upon the charge on the condenser, then current from the source of supply may flow directly to the work along with the stored energy, and thus the quantity of energy supplied to the work varies even though the condenser has been charged to a predetermined voltage. In some instances the recharging of the condenser has been made dependent upon a predetermined time delay from the initiation of the discharge thereof. However, since the duration of the discharge of the condenser may vary over wide limits, the time delay means must be correlated to the particular wave form of the discharge; otherwise the charging current will be supplied to the condenser too soon with resulting variations in the energy supplied to the work, or an unnecessary delay may result between the charging condenser and the discharge thereof resulting in slowing down the operation of the system in effecting a plurality of successive welds.

It is among the objects of the present invention to provide a system of the type described in which the condenser is charged to and maintained at a predetermined potential and in which the recharging current is held off until after the welding current through the transformer has ceased so that regardless of the duration of the current flow through this transformer the supply of charging current to the condenser is blocked as long as current flows in the discharge circuit.

It is a further object of the invention to provide a system in which the same element utilized to control the charging current in response to the voltage on the condenser is also utilized to control the charging current in response to the current flow through the welding transformer of the system.

In systems of the type to which the invention relates, a considerable amount of energy is stored (Cl. 21H) 2 in the system, including the welding transformer at the instant that the condenser is fully discharged. This energy tends to maintain the current flow in the same direction as the original 5 discharge of the condenser and thus tends to charge the condenser in an inverse polarity. This energy may be trapped upon the condenser in the inverse polarity due to the unidirectional nature of the conduction of the tubes controlling the discharge of the condenser through the welding transformer. This energy is lost if the recharging current is supplied to the condenser while the inverse charge exists thereon. If this inverse charge is permitted to reverse itself through the welding transformer, then the welding period is greatly prolonged, while an impulse of low energy content slowly decays therethrough.

It is a further object of the present invention to permit the inverse charge on the condenser to reverse itself through a shunt path lay-passing the welding transformer and to effect the reversal of this inverse charge at the instant that the current to the welding transformer drops to zero and while the supply of charging current to the condenser is still blocked.

In systems of the type to which the invention relates, a considerable amount of residual flux may remain in the metallic core of the welding transformer after the welding operation. This residual flux may vary from weld to weld building up over a number of successive welds. Such variations in the residual flux result in variations of the energy supplied to the work even though the energy stored on the condenser is constant.

It is an object of the present invention to reverse the residual flux of the transformer upon each successive weld. To this end the invention contemplates a system in which the current flows in one direction through the welding transformer to effect one welding operation and flows in the opposite direction through the welding transformer to effect the next succeeding welding operation. A further object of the invention is to provide a system in which the control of charging current to the condenser is effected in response to current flow through the welding transformer regardless of the direction of the current through the transformer.

The above and other objects and features of the invention will be made fully apparent to those skilled in the art from a consideraiton of the following detailed description taken in conjunction with the accompanying drawing in which:

Fig. 1 is a circuit diagram of a welding system assembled in accordance with the present invention; and

Fig. 2 shows a set of curves representing oer tain operating characteristics of said system.

Referring to the drawing, reference numeral indicates the work to which welding current is supplied by way of electrodes E3 and i from the secondary loop 8 of a welding transformer 9 having a primary winding it. The primary winding i0 is provided with end taps H and i2 and a center tap E3. The center tap l3 divides the primary winding it of the transformer 35 into an upper half and a lower half. The welding energy is supplied alternately to the two halves of the primary winding, one complete weld being ef-. fected through one half of the primary winding I 0 and the next succeeding weld being effected through the other half. The welding energy is supplied from a storage condenser M, or from a bank of such condensers. The positive side of condenser I4 is connected directly to the center tap i3,and its negative terminal is connected to both of the end taps H and i2. The connection through the end tap it is by way of a conductor I5, a controlled gaseous discharge device [6, and a conductor ll. The connection to the end tap I2 is by way of a conductor I 8, the gaseous discharge device l9, and conductor 2d. The controlled discharge tubes l8 and it are preferably of the ignitron type having, respectively, anodes 2| and 3! connected to the end taps ii and I2, respectively and mercury pool type cathodes 22 and 32 jointly connected to the negative terminal of the condenser i i. In order to initiate the discharge of the tubes l6 and i9 they areprovided with resistance-immersion ignitors 23 and 33, respectively. In order to supply energizing impulses to the resistance-immersion ignitors 23 and 33, the same are connected by way of gaseous discharge devices 2 3 and 34 to the respective anodes 2i and 35. The discharge device 24% includes an anode 25 connected to the anode 2!, a permanently energized cathode 28 connected to the resistance-immersion type ignitor 23, and a control grid 2?. A current limiting resistor 28 may be provided in the anode circuit 25 to prevent the overloading of device 2 1. The gaseous discharge device it likewise includes an anode connected to the anode H of the tube iii, a permanently energized cathode 38 connected to the resistance-immersion ignitor 33, and a control grid 33'. Acurrent limiting resistor 38 prevents the overloading of the tube t l. Tubes 24 and 34. are normally non-conductive due to a blocking potential applied across the terminals 29 and 3B and 39 and 49, respectively. On removing the blocking potential, which may be effected in a known manner in response to some operation of the welding machine, such as the closure of the electrodes 6 and 7 on the work pieces 5 or the application of welding pressure thereto, either tube 24 or tube 3 3 will fire to supply an igniting impulse to the corresponding ignitor 23 or 33.

In order to charge the condenser i l to a predetermined potential a direct current is supplied thereto from a rectifier including a pair of rectifier tubes 4!. These tubes may be of the gas or vapor filled type having permanently energized cathodes 42. These cathodes-may be thermionic filaments or any other suitable type of cathode. The rectifier tubes i! are provided with control grids 43 and anodes id. The anodes 34 are connected' to the opposite sides of the secondary winding 45 of a power transformer 43 having a primary winding ll. This primary winding 41 is connected at terminals 48 to a suitable source of alternating current.

The two cathodes 1-52 are jointly connected by a conductor 49 to the positive side of the condenser it. A center tap 59 on the primary winding of the transformer it is connected to the negative side of the condenser it through the conductor Hi.

In order to control the potential to which the condenser i4 is charged and prevent recharging of the condenser while current from a preceding discharge is still flowing in the system, the grids 33 are each connected through a resistor 51 to the outer end of the secondary winding 52 of a grid transformer 53 having a primary winding 54. The primary Winding 5 i is supplied with alternating current of the same frequency as that supplied to the primary winding 4! of the power transformer 48. This A. C. voltage is phase shifted by means of a series resistor 55 and a condenser 56 connected across primary 5 of the grid transformer.

In order to supply a blocking potential to grid :33 when the condenser M reaches a predetermined potential, a potentiometer including a resistor 5? is connected across the condenser M.

The adjustable arm or tap 58 of the potentiometer is connected to the negative electrode of a voltage regulating diode 59, the positive electrode of which is connected through a resistor fill of high resistance to the positive terminal of the condenser M. A bridge type rectifier El has its positive terminal connected to the lead between j the resistor til and the Voltage regulating tube 59.

The negative side of the bridge rectifier 6| is connected to the grid circuit at a point between the grid resistors 5i. Preferably, a condenser 62 of about .1 microfarad is connected across the positive and negative terminals of the rectifier.

In order to provide a biasing potential upon the grids 43, whenever current is flowing through the system I provide a potentiometer 63 across one of the halves of the primary winding ill, in

the instance shown, the upper half. The potentiometer 63 is provided with an adjustable arm or tap 64 connected to one end of the primary winding 65 of a transformer ,65 having a secondary winding 61. The opposite end of the .,p1imary winding 65 is connected to the center tap ll! of the primary winding [8. The outer ends of the primary winding 51 of the transformer 66 are connected to the neutral terminals of the rectifier 6!.

In the operation of the voltage regulator and t hold-off system, it will be seen that when there is no charge upon the condenser l4 and when there is no current flow through the primary winding H) of the transformer 9, then no current is flowing through either potentiometer 5? or the potentiometer 63. No voltage exists across the tube 59, and the potential upon the control grid 43 comprises only thealternating phase shift- .ing voltage applied by the grid transformer 53.

. ;Since the grids are either at the same potential .135 the cathodes or positive, the rectifier tubes 4| will fire as soon as the power transformer 48 is energized.

As the condenser M becomes charged, current fiows through the potentiometer 51 causing the tap 58 to become more negative with respect to the positive terminal of the condenser 141.,

Since the tap 58 is connected to the cathode of the voltage regulatortube 59, and the anode of said tube is connected to the positive termine] of the condenser l4, the tube 59 conducts as soon as the potential thereacross reaches its breakdown potential, which is approximately 115 volts. This conduction occurs when a predetermined -vo1tage on'the condenser I4 is reached, as determined by the setting of the potentiometer 51.

The conduction of the tube 59 causes current to flow through the resistor 60. This makes the left-hand side of the resistor 60 negative. This negative voltage applied to the rectifier 6| appears on the grids 43 of the rectifier tubes 4| which blocks them as :sOon as their anode voltage in the course of the alternating voltage applied thereto by transformer 46 falls below their are drop.

Since there is some loss of energy from the condenser l4, particularly after the same :has been charged to the desired predetermined potential, due to the losses through the potentiometer 51 and the tube 59, it is desirable to make up these losses continuously so that at the instant the discharge of the condenser l4 through the welding circuit is initiated the condenser will be at the desired predetermined potential.

To this end I provide for the supply of a continuous trickle of current from either one or both of the tubes 4| of the rectifier during the period when the condenser I4 is charged and awaiting discharge through the welding .circuit. This function is effected by means of the grid transformer '53 which applies an A. C. voltage of approximately 37 volts superimposed on the continuous negative voltage applied from the potentiometer 51. This A. C. voltage is phase shifted by means of the series resistor 55 and condenser 56 so that one or the other of the tubes 4| is unblocked during only a small portion of the half wave of positive potential applied from the transformer 48.

Since the tube 59 always conducts at a definite breakdown voltage, for example 115 volts, it is used as a source of target or reference voltage.

The condenser l4 being charged to predetermined value, the condenser is discharged through the welding circuit by way of one or the other of the tubes l6 and I9. Assuming that it is the turn of the tube [6 to fire to discharge the condenser l4 through the upper winding 10 of the r transformer 9, the blocking potential normally supplied across the terminals 29 and 30 is discontinued in response to the operation of the welding machine while the blocking potential continues to be supplied to the grid 3! of the tube 34 through the terminals 39 and 40. Since at this instant a high potential is applied by the condenser I 4 across the tube 24, this tube fires to conduct an igniting impulse to the ignitor 23 of the tube 16. As shown in Fig. 2, at the time T1 that the condenser charge E0 reaches zero.

the current It through the transformer has passed its maximum. At this time there is no potential applied from the potentiometer 51 across the tube 59 and accordingly the negative blocking potential is not applied to the grids 43 from this source. Unless other means were provided to block the supply of direct current from the rectifier at this time, direct current from the rectifier would be supplied to the welding circuit from the source of supply. Since the series tube IB is conductive at this time it might continue to conduct current from the direct current source indefinitely. .In order to prevent the supply of directcurrent to the system at a time when a charge Ec on the condenser is low and while ourrent is still flowing in the system, I provide a potentiometer 63 across one of the halves of the primary winding IU of the transformer 9, in this instance the upper half. The adjustable tap 64 :of the potentiometer 63 is connected to one end of the primary winding 65 of the transformer :66. The other end of the primary winding 65 is connected to the positive side of the ,condenser l4. The secondary winding 6'! of the transformer 66 is connected to the neutral ter- ,minals of the rectifier 61. Since the negative side of the rectifier 6| is connected to the grid 43 and the positive side of the rectifier is connected through the resistor 60 to the cathodes 42, .a negative bias potential is supplied to the grid 43 as long as current fiows in the primary winding 10, that .is to say, until the time T2. It will be noted that it is immaterial whether the potentiometer 63 is connected across the upper half of the primary winding ill or the lower half thereof. When the current is through the upper half of the primary winding, a voltage is applied directly across the potentiometer 63. When the current is through the lower half of the transformer, a voltage is induced across the upper half. The potentiometer 63 therefore functions to supply a hold-off voltage to the grid 43 as long as current is flowing through the system regardless of whether the welding impulse is directed through the upper half of the transformer or through the lower half. In order to smooth out the pulse of direct current supplied to. the grids 43 through the rectifier 61' from the transformer 68, and for other reasons which will hereinafter appear, a condenser 52 of approximately 0.1 mid. is connected across the positive and negative terminals of the rectifier 6|.

At the time T1 when the charge across the condenser has fallen to zero and the current It is at or'near a maximum, a considerable amount of energy is stored in the welding circuit including the transformer 9. This energy tends to maintain the current in the system in the same direction as previously and thus tends to recharge the condenser 14 in an inverse polarity. At a time T2 when the current It has dropped iczero, the inverse charge on the condenser I4 is at a maximum. Since the series tubes i8 and i9 prevent conduction through the welding circuit in an inverse direction, this inverse charge would normally be trapped on the condenser 14, and the energy represented by the inverse charge would be wasted. In order to conserve this energy I proceed as follows:

.An ignitron $3 is provided in a shunt circuit across the condenser l4 having its anode 69 mm nected to the normally negative side of the condenser l4 and its cathode 79 connected through a reactor H to the normally positive side of the condenser. The cathode 10 is of the mercury pool type and a resistance-immersion i-Znitor 10' is provided for initiating a discharge through the tube 68. In order to supply energizing impulses to the ignitor 10' the same is connected by Wai of a resistor 12 and gaseous discharge device 13 to the anode side of the tube 68. The discharge device 13 includes an anode 14 connected to the anode 69, a control grid 15, and a permanently energized cathode it connected to resistanceimmersion .ignitor it. It will be seen from Fig. 2 that at the time T2 when the current It has fallen to zero and the inverse charge on the condenser I4 is at a maximi'un, the inverse charge will be applied to .the tubes 68 and '13 in a direction in which these tubes are conductive. In order to prevent conduction through the tube 13 until the instant T2 when the inverse charge on the condenser !4 has attained its maximum value, a negative bias is supplied to the grid 15 from a rectifier H having its positive terminal connected to the cathode 75. Since it is desirable that a small amount of current flow through the rectifier Tl as long as a potential exists across the positivemegative terminals thereof, these terminals are connected through a high resistor 78. A potentiometer 19 having an adjustable arm or tap 80 is connected across one of the halves of the primary winding 10, in this instance the lower half. The primary winding 8| of a transformer 82 has one end connected to the tap 80 and its opposite end connected to the normally positive side of the condenser 14. The secondary winding 83 of the transformer 82 has its opposite end connected to the neutral terminals of the bridge rectifier 11.

As long as the current It flows through the welding transformer, a blocking potential is applied to the grid 15 of the tube 13. At the instant T2, when the current It drops to zero, the biasing potential applied to the grid 15 also drops below the cutoif value, and the tube 13 becomes conductive to supply an igniting impulse to the resistance-immersion ignitor 70', whereupon the ignition 68 becomes conductive. Since this instant T2 coincides with the maximum inverse charge upon the condenser 14, the inverse charge is reversed, the current through the shunt circuit being indicated by thecurve IS. The inverse charge on the condenser is reversed during the relative short period of the T3. Although after the time T2 no biasing potential is applied from the transformer 66 by way of the rectifier 6! to the grids 43 of the rectifier tubes 4|, a bias potential is, nevertheless, maintained upon these grids for a period of time at least equal to the duration of the period T2 to T3 by means of the condenser 62. By the time T3 or shortly thereafter the charge on the condenser 62 has dissipated, and the tubes 4| again become conductive to increase the charge on the condenser M to the desired value, which value is pre-' determined by the setting of the potentiometer 5i, and the system is then ready to repeat the operation described in the foregoing in order to effect the next succeeding weld.

It will be evident that where the time required to dissipate the charge on the condenser 62 by way of leakages inherent in the system is materially greater than the duration of the period T2 to T3, the charge may be permitted to leak off more rapidly through a suitable resistor 62. The value of this resistor will be sufliciently high, 100,000 ohms or more, to prevent the charge on the condenser 62 from falling below the voltage required to block the tubes 4! until or shortly after the time T3.

It was assumed in the foregoing that the welding operation described was efiected through the upper half of the primary winding ID by way of the ignitron l6. operation may be effected by way of ignitron l9 through the lower half of the primary winding 1 U of the transformer 9. The operation will be the same as before, excepting upon this occasion the biasing potential on the grid 27 of the tube 24 will be maintained, and accordingly no igniting impulse will be supplied to the ignitron I'5,'and this tube will remain non-conductive. The biasing potential supplied to the grid 31 of the tube 34 will'be discontinued in response to the-operation time between T2 and The next succeeding welding of the welding machine, and, accordingly, the tube !9 will become conductive due to the igniting impulse supplied to the immersion ignitor 33; The tube l9 will, therefore, permit the discharge of the condenser l4 through the lower half of the primary winding ill of the transformer 9.

It will be apparent that it is immaterial to the operation of the device Whether the potentiometer 19 is connected across the lower half of the primary winding ill oracross the upper half, for when the discharge of the condenser 14 is through the lower half of the primary winding 10 current will flow directly through the-potentiometer 19. When the discharge of the condenser I4 is through the upper half of the primary winding I 0 a current will be induced in the lower half of the primary winding, again causing the current to flow through the potentiometer 19. Thus both the potentiometer 63 and the potentiometer 19 may be connected across the same part of the primary winding ill, or a single potentiometer having two taps, one for supplying the current to the primary Winding 65-of the transformer 6i} and the other for supplying current to the primary winding SI of the transformer 82, may be provided, and this potentiometer may be located across either half of the primary winding l0.

While there has been ferred embodiment of the invention other embodiments within the scope of the appended claims will be apparent to those skilled in the art, from a consideration of the embodiment shown and the teachings hereof.

What is claimed is: -1. A welding system comprising a storage condenser, means including a rectifier tube for charg-' ing said storage condenser, a control electrode in said rectifier tube, a welding load circuit, means for discharging said condenser through said welding load circuit in a unidirectional pulse of current during which said storage condenser is charged in an inverse direction, means responsive to the flow of current through said welding load circuit for supplying a blocking potential to said control electrode of said rectifier tube, a shunt circuit across said condenser, means responsive to the termination of said pulse of current for closing said shunt circuit to reverse the polarity of the inverse charge on said condenser thereby partially recharging the same in the original polarity, and a control condenser adapted to be charged in response to said pulse of current to maintain said blocking potential on said control electrode for a predetermined time after the termination of said pulse of current.

2. A welding system comprising a storage condenser, means including a rectifier tube for charging said storage condenser, a control electrode in said rectifier tube, a welding load circuit, means eifective at a predetermined voltage across said condenser for supplying a blocking potential to said control electrode, means for superimposing a phase shifted alternating voltage on said blocking potential, means for discharging said condenser through said welding load circuit herein described a pre a shunt circuit across said the polarity of the inverse means effective at a predetermined voltage across said storage condenser for controlling the current supplied to said condenser from said source, means for discharging said storage condenser through said welding load circuit in a unidirectional pulse of current, means responsive to the flow of current through said welding load circuit for blocking the current supplied to said condenser from said source, and a control condenser adapted to be charged in response to said pulse of current to continue the blocking of the current from said source to said condenser for a predetermined time after the termination of said pulse of current.

4. A welding system comprising a storage condenser, means including a rectifier tube for charging said storage condenser, a control electrode in said rectifier tube, a welding load circuit, means efiective at a predetermined voltage across said storage condenser for supplying a blocking potential to said control electrode, means for superimposing a phase shifted alternating voltage on said blocking potential, means for discharging said condenser through said welding load circuit in a unidirectional pulse of current, means responsive to the fiow of current through said welding load circuit for supplying a blocking potential to said control electrode of said rectifier tube, and a control condenser adapted to be charged in response to said pulse of current to maintain said blocking potential on said control electrode for a predetermined time after the termination of said pulse of current,

5. A welding system comprising a storagecondenser, means including a rectifier tube for charging said storage condenser, a control electrode in said rectifier tube, a welding load circuit, a bridge rectifier, means effective at a predetermined voltage across said storage condenser for supplying a blocking potential to said control electrode through said bridge rectifier, means for discharging said storage condenser through said Welding load circuit in a unidirectional pulse of current during which said storage condenser is charged in an inverse direction, and means responsive to the flow of current through said welding load circuit for supplying a blocking potential through said bridge rectifier to said control electrode of said rectifier tube.

6. A welding system comprising a storage condenser, means including a rectifier tube for charging said storage condenser, a control electrode in said rectifier tube, a welding load circuit, a bridge rectifier, means effective at a predetermined voltage across said storage condenser for supplying a blocking potential to said control electrode through said bridge rectifier, means for superimposing a phase shifted alternating voltage on said blocking potential, means for discharging said storage condenser through said welding load circuit in a unidirectional pulse of current during which said storage condenser is charged in an inverse direction, and means responsive to the flow of current through said welding load circuit for supplying a blocking potential through said bridge rectifier to said control electrode of said rectifier tube.

7. A welding system comprising a storage condenser, means including a rectifier tube for charging said storage condenser, a control electrode in said rectifier tube, a welding load circuit, a bridge rectifier, means effective at a predetermined voltage across said storage condenser for supplying a blocking potential to said control electrode through said bridge rectifier, means for discharging said storage condenser through said welding load circuit in a unidirectional pulse of current during which said storage condenser is charged in an inverse direction, means responsive to the fiow of current through said welding load circuit for supplying a blocking potential through said bridge rectifier to said control electrode of said rectifier tube, and a control condenser connected across the positive and negative terminals of said bridge rectifier adapted to be charged in response to said pulse of current to maintain said blocking potential on said control electrode for a predetermined time after the termination of said pulse of current.

8. A welding system comprising a storage condenser, means including a rectifier tube for charging said storage condenser, a control electrode in said rectifier tube, a welding load circuit, a bridge rectifier, means efiective at a predetermined voltage across said storage condenser for supplying a blocking potential to said control electrode through said bridge rectifier, means for superimposing a phase shifted alternating voltage on said blocking potential, means for discharging said storage condenser through said welding load circuit in a unidirectional pulse of current during which said storage condenser is charged in an inverse direction, means responsive to the fiow of current through said welding load circuit for supplying a blocking potential through said bridge rectifier to said control electrode of said rectifier tube, and a control condenser connected across the positive and negative terminals of said bridge rectifier adapted to be charged in response to said pulse of current to maintain said blocking potential on said control electrode for a predetermined time after the termination of said pulse of current.

9. A welding system comprising a storage condenser, means including a rectifier tube for charging said storagecondenser, a control electrode in said rectifier tube, a welding load circuit, a bridge rectifier, means elfective at a predetermined voltage across said storage condenser for supplying a blocking potential to said control electrode through said bridge rectifier, means for discharging said storage condenser through said welding load circuit in a unidirectional pulse of current during which said storage condenser is charged in an inverse direction, means responsive to the flow of current through said welding load circuit for supplying a blocking potential through said bridge rectifier to said control electrode of said rectifier tube, a shunt circuit across said storage condenser, and means responsive to the termination of said pulse of current for closing said shunt circuit to reverse the polarity of the inverse charge on said condenser thereby partially recharging the same in the original polarity.

10. A welding system comprising a storage condenser, means including a rectifier tube ior char ing said storage condenser, a control electrode in said rectifier tube, a welding load circuit, a bridge rectifier, means effective at a predetermined vol age across said storage condenser for supplying 12. a blocking potential to said control electrode chargedin an inverse direction, means responsive through said bridge rectifier, means for superlmtothe flow of current through said welding load posing a phase shifted alternating voltage on said circuit for supplying a blocking potential through blocking potential, means for discharging said said bridge rectifier to said control electrode of t e Co de ser throu h sa d W d load 5 said rectifier tube, a shunt circuit across said cuit in a unidirectional pulse of current during storage condenser, means responsive to the W ich sa d sto e Co dens s charged in an termination of said pulse of current for closing inve s c o means spo 150 the flOW 0f said shunt circuit to reverse the polarity of the c rre t o gh S We d d Cricuit inverse charge on said condenser thereby par- D y a o g P te ti through said bridge 1 tially recharging the same in the original rectifier to said control electrode of said rectifier polarity and control condenser adapted t b tube, a shunt circuit across said storage concharged in response to Said pulse of current t denser, and means responsive t0 the termination maintain said blocking potential on said control Of Said pulse Of current for closing said shunt Cirelectrode for .a predetermined time after the Quit to reverse the polarity Of the inverse Charge termination of aid pulse of current on said condenser thereby partially recharging A Welding System comprising a storage the same in the original polarity. denser, means including a rectifier tube for 11. A Welding system comprising a storage @011- charging said storage condenser, a control elecdenser, means including a rectlfier tube for trode insaid rectifier tube, a welding load circuit,

charging Said Storage condenser a F' a bridge rectifier, means effective at a predetertrode in said rectifier tube, a welding load circuit,

mined Voltage across said storage condenser for a bridge rectifier, means efiective at a predeter- Supplying a blocking potentialt said tr l mined Volta e ac s Said Storage condenser for electrode through said bridge rectifier, means for supplying a blocking potential Said control superiinposingaphase shifted alternating voltage electrode through said bridge rectifier, means fo on said blocking potential, means for discharging discharging said st r e condenser through Sald said storage condenser through said welding load Welding load C uit i a unidirectional Pulse 9 circuit in a unidirectional pulse of current durcurrent during Whi h s i Storage condenser 18 ing which said storage condenser is charged in an Cha ged i n inverse direction, means responsive inverse direction, means responsive to the fiow of to the flow of current through said Welding load current through Said Welding load Circuit for C rcu t f r s pp y a blocking potential through plying a blocking potential through said bridge said bridge rectifier to said control electrode o rectifier to said control electrode of said rectifier rectifier tube, a shunt circuit aCIOSS Sal-d tub-e a shunt circuit acro said storage c0n SiIO a Condenser, means responsive to the denser, means responsive to the termination of termination of said pulse of current for closing said pulse f current fo closing said shunt said shunt circuit to reverse the polarity of the Quit to reverse t polarity f t inverse charge invers charge on Said Condenser thereby on said condenser thereby partially recharging partially echa i the same in the Original the samein the original polarity, and a control p ari y, and a tr n e s r ad to be condenser connected across the positive and charged in respo se to a d pulse of current to 40 negative terminals of said bridge rectifier adapted maintain said blocking potential on said control t be charg-gd in respgnse t id pulse of current electrode for a predetermined time after the to maintain Said blocking potential on Said term nation o d Pulse of Current trol electrode for a predetermined time after the 1 A We d ys o p s n a storage 0 termination of said pulse of current.

denser, .means including a rectifier tube for I JOHN H. ENGLAND. charging said storage condenser, a control electrode in said rectifier tube, a welding load circuit, REFERENCES CITED a bridge rectifier, means efiective at a predetermined voltage across said storage condenser for 3 2 ifi gfi fii me of resold m the supplying a blocking potential to said control electrode through said bridge rectifier, means for UNITED STATES PATENTS superimposing a phase shifted alternating Number Name Date voltage on said blocking potential, means for dis- 2350 Klemperer Jul 22, 1941 charging said storage condenser through said 5 2,295,293 Rogers Sept 8 1942 welding load circuit in a unidirectional pulse of 5 current during which said storage condenser is 

